1. Field of the Invention
The present invention relates to a recording tape cartridge which rotatably accommodates a reel on which a recording tape, such as a magnetic tape or the like, is wound.
2. Description of the Related Art
Recording tapes, such as magnetic tapes and the like, are used as external recording media of computers and the like. Little space is required for storage of the recording tape, and a large amount of information can be recorded thereon. A so-called single-reel recording tape cartridge is used which rotatably accommodates, within a case, a single reel on which such a recording tape is wound.
Such a recording tape cartridge has a brake mechanism so that the reel does not rotate within the case when the recording tape cartridge is not being used (see, for example, Japanese Patent No. 3187022). A recording tape cartridge equipped with this brake mechanism will be described hereinafter on the basis of FIGS. 12 and 13.
In a recording tape cartridge 200 shown in FIG. 12, a single reel 204 is accommodated within a case 202. The case 202 has a gear opening 206 which is formed at the central portion of a floor plate 202A of the case 202, and a rotation restricting rib 208 which projects downward from a ceiling plate 202B.
The reel 204 has a reel hub 210 which is formed in the shape of a cylinder having a floor, and on whose outer peripheral portion a recording tape is wound. A reel gear 214, which can mesh with a driving gear 212A formed at a rotating shaft 212 of a drive device, is formed in an annular form at the bottom surface of a floor portion 210A of the reel hub 210. Through holes 216, which pass through the floor portion 210A, are provided at a plurality of places which are evenly spaced on a circumference at the region where the reel gear 214 is formed. The diameter of each through hole 216 is greater than the gear pitch of the reel gear 214. Teeth of the reel gear 214 are not provided around each through hole 216.
Anchor projections 218 stand erect at the top surface of the floor portion 210A of the reel hub 210, discretely at plural positions between the through holes 216 which are disposed along a predetermined circumference. A gear tooth 218A is formed at the top end portion of each anchor projection 218.
A disc-shaped braking member 220 is inserted in the reel hub 210. A braking gear 220A, which is annular and which can mesh with the gear teeth 218A, is provided at the bottom surface of the braking member 220. A projection or groove wall portion 222 stands erect at the top surface of the braking member 220. An insertion groove 222A, in which the rotation restricting rib 208 of the case 202 is inserted, is provided at the projection or groove wall portion 222. Due to the rotation restricting rib 208 being inserted in the insertion groove 222A, the braking member 220 cannot rotate with respect to the case 202. The braking member 220 can move in the vertical directions while being guided by the rotation restricting rib 208.
A compression coil spring 224 is disposed between the ceiling plate 202B of the case 202 and the braking member 220. Usually, the braking member 220 is urged downward by the urging force of the compression coil spring 224, such that the braking gear 220A meshes with the gear teeth 218A. In this way, there is usually a rotation locked state in which rotation of the reel 204 with respect to the case 202 is impeded. Further, the reel gear 214 is exposed from the gear opening 206 while the reel 204 is pushed against the floor plate 202A of the case 202 by this urging force.
Moreover, a releasing member 226 is disposed between the floor portion 210A of the reel hub 210 and the braking member 220, so as to abut both. The releasing member 226 has leg portions 226A which are formed in the shape of plates which do not interfere with the anchor projections 218, and which enter into the respective through holes 216.
Due to the braking gear 212A meshing with the reel gear 214, as shown in FIG. 13, the leg portions 226A are pushed by the driving gear 212A against the urging force of the compression coil spring 224, and the releasing member 226 is pushed upward. When the braking member 220 is pushed upward while the releasing member 226 moves away from the floor portion 210A, the meshing of the braking gear 220A and the gear teeth 218A is released. At this time, the reel 204 also floats up from the floor plate 202A, and the reel 204 becomes able to rotate within the case 202.
When the rotating shaft 212 rotates, because the reel 204 rotates within the case 202, the reel gear 214 meshes with the driving gear 212A of the rotating shaft 212. At this time, the releasing member 226 rotates together with the reel 204, and the axially central portion of the releasing member 226 slidingly contacts the axially central portion of the braking member 220. Thus, the axially central portion of the braking member 220 is a convex portion 220B which is formed in the shape of a substantially spherical surface, and substantially point-contacts the axially central portion of the releasing member 226.
On the other hand, when the meshing of the driving gear 212A and the reel gear 214 is released, due to the urging force of the compression coil spring 224, the braking member 220 moves downward, the braking gear 220A and the gear teeth 218A mesh together, and the reel 204 is pushed against the floor plate 202A. In this way, the reel 204 returns to the rotation locked state in which rotation of the reel 204 with respect to the case 202 is impeded.
Although not illustrated, a structure is known which does not have the releasing member 226. In this structure, the convex portion 220B of the braking member 220 is directly pressed by a releasing portion, which projects at the axially central portion of the rotating shaft 212 and enters in from a through hole which passes through the floor portion 210A of the reel hub 210, such that the braking member 220 is pushed upward and the rotation locked state of the reel 204 is released (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 63-251983). A recording tape cartridge having such a structure does not have the anchor projections 218, which are for providing, at positions which do not interfere with the releasing member 226, the gear teeth 218A which mesh with the braking member 220, and the gear teeth are provided in an annular form at the floor portion of the reel hub. However, this structure is the same as the previously-described recording tape cartridge 200 in that rotation of the braking member is impeded by the rotation restricting rib of the case, and in that the braking member is guided by the rotation restricting rib in directions of approaching and moving away from the gear teeth.
However, in the above-described conventional recording tape cartridge 200, in order to permit smooth movement of the braking member 220, a predetermined clearance is provided between the rotation restricting rib 208 of the case 202 and the insertion groove 222A surrounded by the groove wall portion 222 of the braking member 220. Thus, a problem arises in that it is easy for the braking member 220 to tilt with respect to the case 202 (i.e., the reel 204).
Specifically, as shown in FIG. 14A, a maximum angle of inclination θ3 of the braking member 220 with respect to the case 202 (in a case in which the braking member 220 tilts so as to enter in between two of the anchor projections 218) at the time when rotation of the reel 204 is permitted is substantially 2°. As shown in FIG. 14B, when rotation of the reel 204 is locked (e.g., in a case in which the amount of insertion of the rotation restricting rib 208 into the insertion groove 222A is small), a maximum angle of inclination θ4 of the braking member 220 with respect to the case 202 is substantially 6°.
At the time when the recording tape cartridge 200 is not being used (i.e., at the time when rotation of the reel 204 is locked), the braking member 220 tilting greatly in this way becomes a cause of problems in the meshing of the gear teeth 218A and the braking gear 220A. At the time when the reel 204 is driven to rotate, this causes noise or the like due to the region, where the convex portion 220B of the braking member 220 slidingly contacts the releasing member 226, being offset from the axial center of the releasing member 226.
Further, also in the recording tape cartridge which does not have the releasing member 226 and the anchor projections 218, because the other structures thereof are similar to those of the recording tape cartridge 200, a problem which is similar to the above-described problem of the braking member tilting with respect to the case (reel) arises.